Adjust an oven rack to the lower-middle position and pre-heat the oven to 400°F. Line a rimmed baking sheet with aluminum foil.
Brush the oil onto the foil and the cut sides of the squash. Place the squash, cut-side-down, on the foil. Roast until a skewer inserted into the squash meets no resistance, 40 to 50 minutes.
When the squash is almost done, place the butter in a small skillet over medium heat. When the butter melts, add the sage and cook, swirling the pan occasionally, until the butter is golden brown and the sage is crisp, 4 to 5 minutes. Remove the skillet from the heat.
Remove the squash from the oven and turn cut-sides-up. If necessary, cut large pieces in half to yield four pieces. Season the squash with salt and pepper to taste, drizzle with the sage butter, and serve immediately.